Droplet actuators are used to conduct a wide variety of droplet operations. A droplet actuator typically includes two plates separated by a gap to form a chamber. The plates include electrodes for conducting droplet operations. The chamber is typically filled with a filler fluid that is immiscible with the fluid that is to be manipulated on the droplet actuator. Surfaces of the chamber are typically hydrophobic. Introducing liquids, such as aqueous samples, into a droplet actuator loaded with filler fluid can be challenging due to the inherent difficulty of interfacing the droplet actuator with conventional liquid-handling tools as well as the tendency of the hydrophobic chamber to resist the introduction of non-wetting aqueous samples. Typically, a pipette is used to temporarily form a seal with a loading port on the droplet actuator and the liquid is injected under pressure from the pipette, but there are numerous problems with this approach which make it ineffective for untrained users. For example, the pipette must be filled completely to the end, and the seal between the pipette and the loading port of the droplet actuator must be very tight to avoid the introduction of air bubbles or loss of sample. Additionally, the displacement of liquid within the pipette must be very carefully controlled to avoid underfilling or overfilling the droplet actuator. There is a need for an approach to loading fluid onto a droplet actuator which avoids these problems and is simple enough to be used by an untrained user.